Didact. Or whomever activated the rings last time.

: 2. Why did Regret jump the gun and send his ships to Earth before the rest of
: the Covenant.

He thought it was empty. Pretty bad Italian Intelligence.

: 3. What did Truth dig up in the Legendary ending of ODST?

Hopefully a secret tunnel leading to the area under the glass in the Valhalla bases. ;-)

: 4. What questions did the Gravemind ask Cortana, and what answers did she
: give?

Location, location, location. "For a moment of safety, I loosed damnation on the stars."

: 5. If blowing up Halo is enough to stop the flood from spreading, why did the
: Forerunner not just blow up all the Halos? Yay, flood gone!

Local infestation, from the other reply.

: 6. Why does the Covenant hate humanity again?

When the leaders of Earth learned that I refused to cast any humans other than myself in a 137-part massive Elite orgy porn series, the were furious and pulled a Reach on Sanghelios. War!

:-)